A known seat apparatus for a vehicle includes a seat adjustment device adjusting a position of a vehicle seat on which an occupant sits, and a load detection device detecting a load applied to the vehicle seat. A detection result by the load detection device is utilized in a control device for determining whether or not an occupant safety protection device is driven or whether or not the occupant is seated on the vehicle seat. The seat apparatus configured as described above is disclosed, for example, in JP2008-32479A (hereinafter referred to as Reference 1) or JP2001-150997A (hereinafter referred to as Reference 2, refer to a fourth embodiment and FIG. 4). The seat apparatus according to Reference 1 includes a pair of slide rails (upper rails) arranged in a lateral direction of the vehicle and sliding along a longitudinal direction of the vehicle, and load detection devices arranged between each of the slide rails and each of a pair of brackets arranged at respective upper sides of the slide rails along the longitudinal direction to support the vehicle seat. In particular, according to the seat apparatus described in Reference 1, the load detection devices are arranged at four portions that are attachment portions located at respective front and rear end portions of the slide rails arranged in the lateral direction of the vehicle.
According to the seat apparatus according to Reference 2, the number of load detection devices is lower than the number of load detection devices applied in the seat apparatus according to Reference 1 in order to reduce manufacturing, assembling, and wiring costs. The load detection devices are arranged at two portions that are respective attachment portions located between each of rear end portions of a pair of slide rails and each of a pair of brackets in the lateral direction. The bracket and a front end portion of the slide rail are fixed to each other by spot welding and the like.
The magnitude or direction of the load applied to the vehicle seat vary depending on an orientation of the vehicle, an orientation of the occupant, a seated position of the occupant on the vehicle seat, and the like. Accordingly, a load acts on each of the load detection devices in a direction different from a load detecting direction; therefore errors may be included in a detection value of the load detection device. According to the seat apparatus described in Reference 1, the vehicle seat and the slide rails are fixed to one another by the brackets. In addition, each of the brackets is configured to connect the fixed portion positioned at front side of the slide rail to the fixed portion at a rear side of the slide rail. Accordingly, when the magnitude or direction of the load applied to the vehicle seat varies, only a vertical component of force of the applied load relative to a vehicle floor acts on the load detection device. As a result, the errors in the detection value may be reduced.
In addition, for example, the slide rail or a frame that constitutes a portion of the vehicle seat may be deformed depending on the variations of the magnitude or direction of the applied load or depending on an adjusted position of the vehicle seat. At this time, a load acting in a direction to detach the bracket from the slide rail or in a direction to press the bracket against the slide rail may be applied to the fixed portion of the front or rear side of the vehicle seat (slide rail). The load due to the deformation of the slide rail or the frame may be transmitted to the load detection device by the bracket and therefore acts on the load detection device.
Here, in the seat apparatus described in Reference 1, the load applied to the vehicle seat is detected based on a sum total of detection values of the load detection devices arranged at the aforementioned four portions. Accordingly, even when the load due to the deformation of the slide rail or the frame is applied to the fixed portion of the front or rear side of the vehicle seat, variations of the loads acting on the load detection devices are compensated for one another, therefore minimizing influences of the variations on a detection result by the load detection devices. Meanwhile, in the seat apparatus described in Reference 2, the load detection devices are arranged only at the aforementioned two portions. Accordingly, variations of loads acting on the respective load detection devices due to the deformation of the slide rail or the frame may not be compensated for one another. Consequently, errors may be included in the sum total of the detection values of the load detection devices.
A need thus exists for a seat apparatus for a vehicle, which is not susceptible to the drawback mentioned above.